/*********************************************************************
 *
 * Software License Agreement (BSD License)
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 *  Copyright (c) 2008, 2013, Willow Garage, Inc.
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 *     copyright notice, this list of conditions and the following
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 *     with the distribution.
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 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
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 *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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 * Author: Eitan Marder-Eppstein
 *         David V. Lu!!
 *********************************************************************/
#ifndef _GRID_PATH_H
#define _GRID_PATH_H

#include <vector>
#include <global_planner/traceback.h>

namespace global_planner
{

class GridPath : public Traceback
{
public:
    GridPath(PotentialCalculator *p_calc) : Traceback(p_calc) {}

    virtual ~GridPath() {}

    bool getPath(float *potential, double start_x, double start_y, double end_x, double end_y,
                 std::vector<std::pair<float, float> > &path)
    {
        std::pair<float, float> current;
        current.first = end_x;
        current.second = end_y;
        int start_index = getIndex(start_x, start_y);
        // step 1.将目标点的(x,y)作为当前点加入path
        path.push_back(current);
        int c = 0;
        int ns = xs_ * ys_;
        // step 2.进入循环，继续循环的条件为当前点的索引不是起始点
        while (getIndex(current.first, current.second) != start_index)
        {
            float min_val = 1e10;
            int min_x = 0, min_y = 0;
            // step 3.搜索当前点周围8个临近点，选取这8个临近点中potential的值最小的点
            for (int xd = -1; xd <= 1; xd++)
            {
                for (int yd = -1; yd <= 1; yd++)
                {
                    if (xd == 0 && yd == 0) continue;
                    int x = current.first + xd, y = current.second + yd;
                    int index = getIndex(x, y);
                    if (potential[index] < min_val)
                    {
                        min_val = potential[index];
                        min_x = x;
                        min_y = y;
                    }
                }
            }
            if (min_x == 0 && min_y == 0) return false;
            // step 4.将potential值最小的点更改为当前点，并加入path
            current.first = min_x;
            current.second = min_y;
            path.push_back(current);
            if (c++ > ns * 4) return false;
        }
        return true;
    }

};

} //end namespace global_planner
#endif
